feat(lanes): add POST /:id/agents/install route (E3)

server/routes/lanes.js

@@ -33,6 +33,7 @@ const {
 } = require("../lib/worktree");
 const { withLaneLock } = require("../lib/lane-lock");
 const { checkSync, mergeSync, continueSync } = require("../lib/lane-sync");
+const { installAgents } = require("../lib/lane-agents");
 const { HOOKS, runHook, resolveProfile } = require("../lib/lane-profile");
 const { slotDirs } = require("../lib/lane-slots");
 const {
@@ -328,6 +329,26 @@ router.post("/:id/proof-link", sameOriginGuard, (req, res) => {
   res.json(proofLib.ensureProofLink(lane));
 });
 
+/**
+ * Install the ship-feature-lane pipeline's agent templates (qc-local,
+ * senior-gate-reviewer) into this lane's own .claude/agents/. Static file
+ * copy — no templating, no credentials to inject (this repo has no
+ * seed-account system yet; see the E3 design spec's Decisions table).
+ * Never automatic, same as proof-link: a session calls this explicitly.
+ */
+router.post("/:id/agents/install", sameOriginGuard, async (req, res) => {
+  const lane = lanesLib.getLane(req.params.id);
+  if (!lane) return res.status(404).json({ error: { code: "ENOLANE", message: "lane not found" } });
+  try {
+    res.json(await installAgents(lane));
+  } catch (err) {
+    if (err.code === "ENOTGITREPO") {
+      return res.status(400).json({ error: { code: err.code, message: err.message } });
+    }
+    res.status(500).json({ error: { code: err.code || "ERUNTIME", message: err.message } });
+  }
+});
+
 /**
  * A lane's working-copy facts: branch, short HEAD, that commit's subject, and
  * the uncommitted counts. Read-only, so no same-origin guard — that guard